Geochemical characterization of Malm Zeta laminated carbonates from the Franconian Alb, SW-Germany...

Geochemical characterization of Malm Zeta laminated carbonates

from the Franconian Alb, SW-Germany (II)

L. SCHWARK1*, M. VLIEX1 and P. SCHAEFFER2

1Geological Institute, University of Cologne, ZuÈ lpicher Str. 49a, 50674 Cologne, Germany and 2Institutde Chimie, UniversiteÂ Louis Pasteur, 1 rue Blaise Pascal, 67000 Strasbourg, France

AbstractÐDuring Jurassic times, especially within the Malm z stage, local depressions formed on theEastern Bavarian Carbonate Platform that were surrounded by wall reefs. This created a unique deposi-tional environment, where in an open-marine setting stagnant and anoxic bottom waters developed inan intra-reef depression. Anoxic conditions were stabilized below wave base by enhanced salinity in thebottom waters and establishment of a density strati®cation. Biomarker analysis was applied to charac-terize palaeosalinity and redox conditions, utilizing organic sulfur compound, methylated chroman,hopanoid and saturated isoprenoid distributions. Prevention of terrigenous in¯ux by protecting reefwalls lead to iron de®ciency in intra-reefal sediments causing early diagenetic sulfurization of functiona-lized lipids. Absence of clay-mineral catalysts and early sulfurization favored an unusual steroid distri-bution lacking rearranged analogues but providing coexistence of saturated steranes with baa-, aaa-and abb-con®guration, D13(17)-spirosterenes, unknown sterenes and steradienes as well as mono-, di-and triaromatic steroids. Desulfurization of the polar fraction was carried out for two samples to verifythat palaeoenvironment reconstruction based on free hydrocarbon and heterocompound distributionwas not invalidated by sulfur quenching of selected compounds. Gammacerane was found to be theonly component to occur exclusively in the sulfur-bound fraction. Only minor amounts of hydrocar-bons were released upon desulfurization implying that free bitumen analysis was applicable for organo-facies characterization. Organic petrological investigation of organic mats revealed the presence of twodi�erent types of such structures. Comparison of organoclast ¯uorescence spectra with those ofextracted porphyrin fractions indicate an origin of porphyrins exclusively from cyanobacterial matswhereas algal dominated mats yield no porphyrins. This aims towards a better localization of speci®cbiomarker origin in geological samples. # 1998 Elsevier Science Ltd. All rights reserved

Key wordsÐJurassic, Malm, Solnhofen Lithographic Limestone, marls, cherts, limestones, palaeoenvir-onment reconstruction, palaeosalinity, organic sulfur compounds, aromatic steroids, sterenes, spiroster-enes, steradienes, hopenes, porphyrins, ¯uorescence properties

INTRODUCTION

The Jurassic age lithographic limestone of the

Solnhofen area, Franconian Alb in SW-Germany

(Fig. 1), is well known for its excellent preservation

of fossils. Vertebrates like Archeopterix, the earliest

bird and Compsognathus, known to be the smallest

dinosaur, were found in the well laminated micritic

limestones of the Solnhofen and Jachenhausen area.

The exquisite preservation of fossils and the extre-

mely ®ne lamination of the matrix rocks indicate

exceptional conditions of sedimentation for the car-

bonates, pointing towards a low energy and poss-

ibly anoxic environment. Several palecological

models have been established, based on micro- and

macrofossil faunal assemblages to de®ne, for

example, water circulation and strati®cation pat-

terns, autochthonous productivity and terrigenous

in¯ux, redox and salinity conditions (von Freyberg,

1966, 1968; Barthel, 1970, 1978; Keupp, 1977, 1994;

Keupp et al., 1993). Reconstruction of palaeoenvir-

onmental conditions by means of organic geochem-

istry, however, is usually hindered because the

entire area was subjected to uplift and erosion

during the Early Cretaeous and late Tertiary, allow-

ing groundwater to penetrate into the limestones

and thus causing oxidation of the organic matter,

especially in the Solnhofen area (Meyer and

Schmidt-Kaler, 1993).

In order to overcome the problem of weathering,

we investigated a core from the Rennertshofen

Trough, south of Solnhofen, where the organic mat-

ter embedded in the Malm limestone was preserved,

allowing for reliable organofacies characterization.

Molecular indicators for palaeoenvironmental

reconstruction in carbonatic/evaporitic depositional

settings, previously developed during phases I and

II of the ENOG programme (ENOG: European

Network of Organic Geochemists; see Huc and

Sinninghe DamsteÂ , 1993; Leythaeuser and

Sinninghe DamsteÂ , 1995) were applied to character-

ize organic matter incorporated in the Malm z sedi-

ments, in order to verify or re®ne and improve

existing palecological models. This is also regarded

Org. Geochem. Vol. 29, No. 8, pp. 1921±1952, 1998# 1998 Elsevier Science Ltd. All rights reserved

Printed in Great Britain0146-6380/98 $ - see front matterPII: S0146-6380(98)00192-2

*To whom correspondence should be addressed. E-mail:[email protected]

1921

as a test, whether molecular palaeontology couldcontribute to improve environment characterizationin a case where micro- and nannofossil evidence is

limited due to dissolution and in part replacementcrystallization of fossil shells and test (Keupp et al.,

1993; Meyer and Schmidt-Kaler, 1994).In part I of this publication we described in more

detail the geological setting, the basic organic pet-rology and the inorganic and bulk organic geo-

chemistry. In the present contribution we focus onthe biomarker geochemistry to obtain informationabout palaeoenvironmental conditions during sedi-

mentation of the Malm carbonates. We examinedthe composition of the ``free'' solvent extractable

bitumen, including aliphatic and aromatic hydrocar-bons as well as organic sulfur compounds (OSC).In order to account for a potential strong bias in

lipid distribution due to early sulfur incorporation,the polar bitumen fractions of two samples were

desulfurized and the distribution of released hydro-carbons compared with those of the ``free'' bio-

marker composition.

Aiming towards a better coupling of microscopi-cal observations with biomarker geochemistry andan improved understanding of the exact localization

of speci®c extractable compounds within a sedimentsample, we investigated the relationship betweenspectral ¯uorescence characteristics of solventextractable porphyrins and the ¯uoresence proper-

ties of organoclasts and bitumens.

EXPERIMENTAL

Organic petrology

Whole block samples were cut perpendicular tobedding, embedded in epoxy resin and polished.

Organic petrographical investigations were deter-mined by re¯ected light in oil immersion using aZeiss Axioplan microscope using magni®cations of

200� and 500� .The mean random vitrinite (Rr%) or solid bitu-

men re¯ectance (Rb%) was measured to determine

the maturity of organic matter. The measurements

Fig. 1. Location map of study area in southern Germany.

L. Schwark et al.1922

were carried out in comparison to a Saphir stan-dard of Rr=0.500% (546 nm, oil immersion) apply-

ing the methods of DIN 22020 (1986). Bitumenre¯ectance (Rb) was converted into vitrinite re¯ec-tance using the equation of Jacob (1989):

Rv=0.618Rb+0.40 (%, oil). This equation wasestablished for Palaeozoic and Mesozoic rocksamples from the Saxonian Basin of Northwest-

Germany.Spectral ¯uorescence measurements were carried

out with the same equipment but under illumination

applying a HBO 100 W lamp (Zeiss). A spectrum ofa stabilized tungsten lamp served as ¯uorescencestandard and intensity was normalized to an uranylglass (GG-17, 1 mm) at 535 nm. ICI-colourmetric

values were determined after DIN 5033 (1979) andplotted into a two dimensional chromatographicdiagram after DIN 6164 (1978) (for details of the

procedure, see Hagemann and Hollerbach, 1986).

Carbon and sulfur determination and Rock-Eval py-

rolysis

The contents of total carbon (TC) and total sul-fur (Stot) were determined with a LECO CS225 ana-

lyser. The same instrument was used for totalorganic carbon (TOC) measurements after removalof carbonate minerals with hydrochloric acid (32%

v/v) and repetitive washing with distilled water.Carbonate contents were calculated by di�erenceand expressed as percent CaCO3. Rock-Eval analy-

sis was performed according to the methoddescribed by EspitalieÂ et al. (1977) and Bordenave(1993) with a VINCI Rock-Eval-II Analyser. S1, S2

and Tmax-values were measured and corresponding

HI, OI and PI values calculated.

Extraction and chromatography

Finely ground (<0.2 mm) samples were extractedusing a DIONEX ASE 200 extractor with dichloro-

methane for 20 min under a pressure of 50 bar at atemperature of 758C. Total extracts were separatedinto maltenes and asphaltenes by precipitation witha 40 fold excess of n-hexane. Maltenes were separ-

ated into fractions of aliphatic hydrocarbons, aro-matic hydrocarbons and heterocomponents byMPLC (Radke et al., 1982).

Free hydrocarbon analysis

GC±MS analysis of the saturated and aromatichydrocarbons was carried out using a HP 5890Series II gas chromatograph coupled to a HP 5989single quadrupole mass spectrometer. A

50 m*0.20 mm (ID) fused silica column (HP 5),coated with 5% chemically bonded phenyl±methyl±silicon (0.33 mm) was used with helium carrier gas.

The GC oven temperature was programmed from70 to 1408C at a rate of 108C/min followed by asecond gradient from 140 to 3208C at 38C/min. The

mass spectrometer operated in EI mode at 70 eV

with a scan range from m/z= 30 to 600 for identi®-cation of individual compounds of the aliphatic and

aromatic hydrocarbon fractions. Data acquisitionand processing was performed using a HP MS-ChemStation data system. Peak identi®cation was

carried out by comparison of mass spectra withthose of the system library and by comparison withpublished spectra.

Desulfurization experiments

Fractionation. The Raney nickel desulfurization

experiments were carried out on the polar fractionfrom the organic extract of two samples (sampleM110 and sample ML69). Brie¯y, the precipitated

asphaltenes (ca. 100 mg) were adsorbed on silica geland loaded on a silica gel column. A ®rst elutionwith a hexane/dichloromethane mixture (7:3 v/v)yielded some occluded free hydrocarbons and small

amounts of nickel porphyrins (ca. 10±15 mg/g or-ganic extract). A second fraction was then recov-ered by elution with a dichloromethane/methanol

mixture (3:1 v/v), yielding ca. 700±800 mg/g organicextract of polar material.Raney nickel desulfurization of a polar chromato-

graphic fraction. The polar chromatographic frac-tion (see above) of the organic extract was dissolvedin a 1:1 mixture of toluene/ethanol and an excess ofRaney nickel, preextracted with distilled water and

ethanol, was added. The mixture was re¯uxedunder argon for 3 h, after which the supernatantwas recovered. The Raney nickel was extracted with

dichloromethane (�2), the organic extracts com-bined and the solvent removed under reduced press-ure. Puri®cation of the extract by liquid

chromatography (silica gel, hexane as eluant)yielded an (alkane + alkene) fraction (Rf>0.8; ca.15 mg/g polar fraction). The aromatic hydrocarbons

(ca. 25 mg/g polar fraction) were recovered byelution with a hexane/dichoromethane mixture (8:2v/v).Gas chromatography. The hydrocarbons recovered

by Raney nickel desulfurization were analysed on aHewlett Packard gas chromatograph (HP 6890series) equipped with an on-column injector, a FID

detector and a HP5 column (30 m�0.32 mm i.d.;0.25 mm ®lm thickness). H2 was used as carrier gasand the oven was programmed from 70 to 2008C(108C/min), 200 to 3008C (48C/min), then held iso-thermally for 30 min.Gas chromatography±mass spectrometry. Analyses

of the hydrocarbons released by desulfurization

were performed on a Varian 3400 gas chromato-graph equipped with a programmable on-columninjector and a DB5 fused silica column

(30 m�0.25 mm; 0.2 mm ®lm thickness) connectedto a Finnigan MAT INCOS 50 mass spectrometeroperating at 70 eV. The oven temperature was pro-

grammed from 70 to 2008C at 108C/min, 200±

Geochemistry of Malm carbonates 1923

3008C at 58C/min, then held isothermal at 3008Cfor 30 min. He was used as carrier gas.

Carbon isotopic analysis

After organic solvent extraction, determination ofbulk kerogen carbon isotope composition was per-

formed on a Finnigan Delta S mass spectrometer.Standard notation in d13C (-) values relative to thePDB-standard was used. Prior to measurement ofthe organic carbon isotopes all carbonate minerals

were quantitatively removed by treatment with hy-drochloric acid.

RESULTS

Organic petrology and spectral ¯uorimetry ofextracts and porphyrin fractions

The basal interval of the studied core section(Fig. 2) below 135 m belongs to the Malm z1(Meyer and Schmidt-Kaler, 1994) and contains thetypical ``lithographic limestones'', i.e. white to bu�coloured micritic limestone, with excellent beddingand no internal texture (in the following abbre-

viated KW). The micrites are exclusively composedof individual calcite crystals, 1±10 mm in size.Isolated dino¯agellates and coccolithes are enclosed

within the matrix. Pyrite is only present in minoramounts and of diagenetic origin. In all samples ofthe Malm z 1 studied no particulated organic mat-

ter could be detected.

The interval comprising the Malm z 2 (135±67 m)

and z 3 (67±25 m) stage consists of a sequence of

grey and bu� coloured micritic limestones (abbre-

viated as K), which are interbedded with brownish

bituminous, very ®ne laminated marls (ML). Within

the Malm z 2 chert layers (KK) of 1±10 mm thick-

ness occur between 80 and 110 m depth (Fig. 2).

Slumping structures and disturbance of sediment is

observed for the Malm z 3 sediments.

The bituminous marls (ML) of the Malm z 2 and

z 3 show an intensive mm-scaled lamination.

Laminae of ®ne grained carbonate minerals (mainly

calcite) alternate with dark brown laminae com-

posed of a mixture of clay minerals and organic

matter. These shaly layers are rich in framboidal

pyrite formed by bacterial sulphate reduction

(Berner, 1983). The relative amount of pyrite

increases from bottom to top. In the iron-limited

depositional environment of the Rennertshofen

Trough this more likely indicates an increase in the

supply of terrigenous derived dissolved iron than an

increase of anoxicity during sedimentation.

The organic matter of the laminated limestones

shows microscopically identi®able marine and some

very minor terrestrial organic constituents.

Terrestrial organic matter consists of some isolated

tissues with preserved cell structures but preferen-

tially of reworked vitrinitic organoclasts. Main con-

stituents of the marine organic matter within

laminated limestones are unicellular thick-walled

Fig. 2. Stratigraphic cross section of the Upper Malm in South-Germany with schematic representationof reef and trough facies, adopted from Meyer and Schmidt-Kaler (1993).


Fig. 3. Spectral colourimetry diagram according to DIN 6164 showing two clusters of data points.Cluster one comprises the alginites and porphyrin-free maltene fractions, cluster two contains cyanobac-terial mat derived red bituminites and the free extractable porphyrins. Porphyrins therefore predomi-

nantly originate from cyanobacterial mats.


tasmanites type algae >50 mm in size. They are ran-

domly distributed in the carbonatic sediment or

enriched within the shaly laminae as mats elongated

parallel to bedding. Under blue light excitation the

algal mats and the associated exudated bitumen

reveal an intensive green to yellowish ¯uorescence

indicating low thermal maturity.

In some cases the associated bitumen is of a red

¯uorescence colour and has a negative alteration, a

characteristical feature for the presence of chlorins/

porphyrins within the mats. Keupp (1977), Barthel

(1978), Keupp et al. (1993) and Keupp and

Neumann (1996) proposed a cyanobacterial origin

for the organic mats in case of the laminated lime-

stones from the Solnhofen area, which is located

some tens of kilometers north of the Rennertshofen

Trough. An additional input of cyanobacterial mat-

ter to the algae-bearing mats thus seems likely, but

is impossible to determine by microscopical obser-

vation. In contrast to the shaly laminae, the carbo-

natic laminae of the laminated limestones include

only a few isolated tasmanites type algae and dino-

¯agellates, which include some bitumens with yel-

low ¯uorescence colour.

Especially within the Malm z 2 interval the lami-

nated limestones are interbedded with black cherts

of 1±10 mm in thickness (in the following labelled

MK). The carbonate minerals and organic matter

in those cherts show the same appearence as in the

laminated marls. The cherts are, however, enriched

with spherical radiolaria, 1±10 mm in size and the

matrix and intergranular cavities show a secondary

cementation with amorphous silica. RFA analyses

of chert samples indicate high amounts of SiO2 and

extremely low Al2O3 contents (Vliex and Schwark,

1998). The resulting SiO2/Al2O3-ratios by far exceed

average shale values also indicating a biological ori-

gin of the amorphous silica (Brumsack, 1988), i.e.

from dissolved radiolaria, now often replaced by

carbonate, and from siliceous sponges. Under blue

light excitation the radiolaria o�er a green to yellow

¯uorescence colour that argues for a good preser-

vation of bitumen within the organoclasts. No

microscopical observations of diatomaceous algae

were made and no indications of their presence in

Malmian samples exist in the literature.

Microscopical ¯uorescence measurements were

made on solitaire alginite and red coloured streaky

bituminite within polished block samples. The same

technique was applied to chromatographically sep-

arated Ni- and V.O-porphyrin and porphyrin-free

maltene fractions. Fluorescence spectra of the uni-

cellular tasmanites type algae (type A) were

measured for wavelength intervals from 450 to

700 nm. Main intensities are recognised for the

green range (500±510 nm) of the spectrum, whilst

intensities in the yellow and red range of the spec-

trum (600±650 nm) are low. The visual impression

of a greenish to yellow ¯uorescence colour is also

re¯ected by a red/green ratio varying from 0.23±

0.09. In some cases the same algae illuminate with

bright intensities in the range of 470 nm and exhibit

a light bluish colour (type B). After Hagemann and

Hollerbach (1986) this colour corresponds to high

contents of aliphatic hydrocarbons.

In the case of the organic mats characteristic of

the laminated marls, the visual impression is that of

a reddish colour. The associated ¯uorescence spec-

trum contains two maxima of intensity. The ®rst

one occurs in the range of green to yellow and the

second one between 620 and 720 nm. The spectrum

is the result of a mixture of the ¯uorescence beha-

viour of tasmanites type algae and exsudated red

coloured liquid bitumen. After extended illumina-

tion (>2 min) the red colour shows a strong nega-

tive alteration and only the yellow colour of algae

remains (Vliex and Schwark, 1998). This intensive

red ¯uorescence colour and the strong negative

alteration are characteristical criteria for chloro-

phylls or fossil chlorins/porphyrins.

To verify this observation porphyrin and por-

phyrin-free maltene fractions were isolated by liquid

chromatography and analysed by spectral ¯uor-

escence measurements. The spectra of isolated V.O-

porphyrin fractions comprise a single maximum in

the red range (725 nm) while Ni-porphyrins with

some admixture of V.O-porphyrins reveal an ad-

ditional maximum in the range of 650 nm (red). In

both cases no intensities are recognised within the

green to yellow range of the spectrum.

For a quantitative comparison of the ¯uorescence

properties of algae, bituminites and isolated extract

fractions, the colorimetric values x and y were cal-

culated following DIN 6164 and plotted in Fig. 3.

The ¯uorescence colours of the measured objects

are separated into two clusters. The ®rst cluster

occurs between colour shade lines 21 and 23, repre-

senting the tasmanites type algae of type A and B.

The same ¯uorescence properties were determined

for the porphyrin-free maltene fractions. After

Hagemann and Hollerbach (1986) the position of

this cluster in the discrimination diagram corre-

sponds to that of oils and extracts of low thermal

maturity.

The second cluster is composed of data points

from isolated Ni- and V.O-porphyrin fractions and

is located between the colour shade lines 1 and 5 in-

dicating orange to red colours. This cluster also

contains the data points for red coloured liquid

bitumens, exclusively found in organic mats occur-

ring in laminated marls (Fig. 3).

These results indicate that tasmanites type algae

do not account as a source for the porphyrins

extracted from the laminated limestones. According

to the ¯uorescence behaviour, a close spatial re-

lationship between the occurrence of porphyrin bio-

marker compounds in the extracts and the red-

coloured organoclasts exclusively occurring with the


ML organic mats is attributed to a cyanobacterialcontribution. The ¯uorescence spectrum of these

red streaky bitumens from the bacterial mats showsidentical intensity maxima in the long wave rangeof the spectrum and the same strong negative

alteration as compared to the porphyrin fractions.After Keupp (1977, 1994) and Keupp et al.

(1993) the organic mats of laminated limestones

from the nearby Solnhofen area are composed ofalgae and an additional cyanobacterial input. Theauthors proposed episodic bacterial blooms as a

likely process for the formation of the organicmats. Meyer and Schmidt-Kaler (1994) relate thesedimentation of laminated marls and limestones to``rhythmic algal blooms''. Our results con®rm that

two types of organic mats are present, one com-posed almost exclusively of algae and the othermat-like structures preferentially originate from cya-

nobacteria with algal input in those intervalsstrongly reduced. Algal mats that are mainly pro-duced by Tasmanales-like algae do occur frequently

in the Malm carbonates and may represent regularmarine conditions whereas cyanobacterial matswere build under stressed conditions.

Random re¯ectance measurements have been car-ried out on solid bitumen in order to determinethermal maturity of organic matter in Malmsamples. Re¯ectance values of laminated limestones,

cherts and lithographic limestones are plotted inre¯ectance frequency histograms (re¯ectograms) inFig. 4. In case of the laminated marls (ML) re¯ec-

tance values extend from 0.1 to 0.9% Rb. The max-ima of the unimodal distributions range between0.35 to 0.40% Rb indicating a very low degree of

thermal maturity. In contrast to laminated marls,the nonlaminated carbonates (K) show polymodaldistributions of the re¯ectance classes. The valuesrange up to 1.5% corresponding to vitrinitic and

inertinitic organoclasts of a reworked origin. Inthese samples the terrestrial input is also dominatedby solid bitumen, which shows the same maxima as

the laminated limestones.

Bulk parameters

Bulk parameters determined on an extended

sample set are described by Vliex and Schwark(1998) and therefore, only a short summary is givenhere. The TOC-content is lowest in the pure white

carbonate samples with 0.1±0.5% and in all othersamples ranges from 0.3 to 15% TOC with no sig-ni®cant control by lithofacies. Total sulfur valuesshow excellent positive correlation with TOC and

vary between 0.05 and 3.0% TS. The C/S-ratio onaverage calculates to 3.2 and indicates a high pro-portion of organically bound sulfur as given by the

low Fe/S-ratios of on average 0.05 documentingthat only a minor fraction of the sulfur is bound toiron-sul®des. Excellent quality of the organic matter

is revealed by HI-values ranging from 100 to 1050

(mg HC/g TOC), most samples clustering aroundHI-values of 600 to 800 (mg HC/g TOC). In agree-

ment with microscopical analysis a type II marinealgal kerogen can be attributed to most samples.Extremely lipid-rich samples of type I-kerogen are

characterized by TOC-values below 2.0%. Rock-Eval maturity estimation of organic matter withTmax values of 400 to 4108C and PI-values of <0.1

con®rms the microscopically deduced low matu-ration level. Isotopic characterization of the kero-gens gives d13C ratios ranging from ÿ25.8 to

ÿ29.5- with most values between ÿ28.0 andÿ29.0-, typical of Jurassic marine organic matter.Extract yields show a dependency on lithologies

with limestones and cherts yielding less than

1000 ppm, whereas marls and siliceous carbonateson average provide between 400 to 4000 ppm withseveral samples in the range of 5000 to 16500 ppm.

Due to the low thermal maturity only between 10and 25% of the extractable bitumen is composed ofhydrocarbons.

Biomarker composition

Discussion of biomarker composition follows theclassi®cation into three main lithofacies types micri-

tic limestones, marls and cherts as previouslyreported (Vliex and Schwark, 1998). Where appli-cable, a more detailed grouping into sub-lithofacies

types of white (KW) and grey limestones (K), lami-nated (LM) and non-laminated marls (M) and alter-nations of chert layers (KK) with marls (MK) was

used. Distribution of free lipids is applicable forpalaeoenvironment characterization, even at the lowmaturity of 0.3% Rr because desulfurization exper-iments with Raney Nickel gave very low yields and

hence no strong bias in biomarker distribution dueto sulfur-bonding occurs. The free lipid distributionis therefore discussed ®rst and in detail, followed by

supplementary information derived from desulfur-ized polar fractions.

Free aliphatic hydrocarbons

The fraction of the free aliphatic hydrocarbonspredominantly consists of n-alkanes and acyclic iso-prenoids for most samples. Only for a few samples

of the LM lithofacies type, cyclic terpenoids domi-nate the aliphatics. Reduced amounts, sometimesonly traces, of unsaturated and saturated steroids

and hopanoids occur within the K and KW facieswhereas the M and LM marls are generallyenriched in cyclics that often dominate over the n-alkanes. The KK and MK chert are almost devoid

of hopanoid and steroid biomarkers. Bi-, tri-, ortetracyclic sequi- or diterpenoids are lacking in allsamples. Comparably, tricyclic and tetracyclic triter-

penoids could not be detected but in trace amounts.Distribution of n-alkanes. Solvent extractable ali-

phatic hydrocarbons of the three lithofacies-types

limestones, marls and cherts contain a series of


homologous n-alkanes. Pure cherts are character-

ized by a very smooth n-alkane distribution ranging

from n-C12 to n-C35, maximising at n-C15 and show-

ing a very minor predominance of n-C21 and n-C23

over the neighboring even numbered n-alkanes. Sili-

ci®ed limestones give a comparable distribution in

Fig. 4. Solid bitumen re¯ectograms for three di�erent lithofacies types. MK 122 represents a silici®edcarbonate or chert layer, K11 originates from a lithographic limestones and ML45 is representative ofthe laminated marl lithofacies type. Laminated marls always show a narrow unimodal distribution of

low re¯ectance values around 0.35% Rb indicative of an thermally immature sediment.


the C20+ range with additional high contributions

of even numbered short chain n-alkanes (Fig. 5).

Limestones show n-alkanes ranging from n-C12 to

n-C35 with a pronounced predominance of short

chain even-numbered n-alkanes C14, C16, C18 and to

a lesser extent n-C20. In all KK and KW samples n-

C16 is the most abundant n-alkane. Comparable to

the chert samples, a minor preference of n-C23 and

n-C25 in relation to n-C22, n-C24 and n-C26 is noted

(Fig. 5). Marls showing a much higher lithological

variability are consequently also characterized by

more diverse n-alkane distributions. Non-laminated

marls and silici®ed marls more closely resemble the

distribution noted for limestones, i.e. predominance

of even-numbered n-alkanes in the C14 to C18

range. This feature was not observed for laminated

marls that instead reveal a shift in n-alkane distri-

bution to compounds with longer chain length max-

imising at n-C23 and a preference of odd- over

even-numbered n-alkanes in the C21 to C35 range

(Fig. 5). The silici®ed marls di�er from the non-

laminated marls by showing a predominance of n-

C14 instead of n-C16 as for the latter, by higher rela-

tive contribution of compounds in the C21 to C35

domain and a more pronounced odd over even pre-

dominance in that range.

The n-alkane distribution for all samples thus in-

dicates a fully marine origin for all samples with

virtually no terrigenic input of plant wax derived n-

alkanes. Although deposition in the Rennertshofen

Trough occurred in a shallow water environment

and close to the continent, this is in agreement with

the palaeogeographical situation. Terrigenous input

very e�ectively was restricted by the coral, algal

and spongal reefs providing a perfect barrier sur-

rounding the intra-reef depocenter (Meyer and

Schmidt-Kaler, 1989, 1994; Vliex and Schwark,

1998).

The strong dominance of short chain even num-

bered alkanes (odd over even predominance = 0.2±

0.5 in the C12 to C20 range) argues for a carbonatic

anoxic environment (Hite et al., 1984; Palacas et

al., 1984; ten Haven et al., 1985, 1988; Connan et

al., 1986; Peters and Moldowan, 1993; de las Heras

Fig. 5. Fragmentograms of m/z = 85 for 4 di�erent lithotypes illustrating low end biased distributionof isoprenoid and n-alkanes for cherts (MK122) and limestones (K116) as opposed to long-chain domi-nated non-laminated (M125) and laminated (ML26) marls. Numbers indicate chain length of n-alkanes

or isoprenoids, e.g. pristane, phytane, PME, squalane and lycopane.


et al., 1997). Short chain even-numbered n-alkanes

have been reported from various marine and lacus-

trine systems spanning a wide range of salinities,

where they were related to microbial sources (e.g.

Grimalt and Albaiges, 1990). Even carbon number

preference of n-alkanes is also associated with

enhanced salinity environments (Palacas et al.,

1984; Moldowan et al., 1985; ten Haven et al.,

1985, 1988). Sheng et al. (1980) suggested, that the

reason for the dominance of even numbered alkanes

is a complete reduction of fatty acids. Alternatively,

a selective preservation of naturally occurring even

numbered n-alcohols and alkyl-esters by incorpor-

ation in the high molecular polar fraction by sulfur-

bounding can occur (de Leeuw and Sinninghe

DamsteÂ , 1990). The short chain n-alkanes may orig-

inate from marine algae and from cyanobacteria.

Cyanobacteria are reported to produce no car-

boxylic acids and n-alkanes extending beyond n-C18

(Volkman and Maxwell, 1986). Hence, the long-

chain n-alkanes of the Malm z samples must be de-

rived from marine algae with some very minor con-

tribution from land plant waxes. This is based on

microscopical investigations and the low amounts

of plant wax derived n-C27, n-C29, n-C31 as com-

pared to n-C21, n-C23 and n-C25 alkanes. No prefer-

ence of medium chain length even-numbered n-

alkanes n-C22 and n-C24, characteristic of several

carbonatic/evaporitic systems studied by ten Haven

et al. (1985, 1988) was noted.

The predominance of n-C23 and adjacent odd-

numbered n-alkanes is similar to the one observed

for other Jurassic rocks, especially those of the

Posidonia Shale or Kimmerdige Clay Fm.

(Farrimond et al., 1984; van Kaam-Peters et al.,

1997). An excursion to heavier d13C-values for this

particular compound as compared to the adjacent

n-alkanes in the Kimmeridge Clay Fm. suggests an

origin from highly specialized algae (van Kaam-

Peters and Sinninghe DamsteÂ , 1997). In analogy, a

signi®cant change in the algal association for the

marl and limestone lithotypes of the Malm z car-

bonates has to be invoked. As a precursor com-

pound for the n-C23-alkanes is still unknown, the

type of algae preferentially contributing to the free

lipids of the marl lithofacies samples could not be

determined.

Free isoprenoid alkanes. Regular isoprenoid

alkanes in the Malm z samples include farnesane

(low amounts), i-C16, norpristane, pristane, phy-

tane, i-C21, PME (2,6,10,15,19-pentamethyleico-

sane), squalane and lycopane. No highly branched

C20 to C25-isoprenoids, often found in carbonatic

evaporitic systems were detected and thus an input

from diatoms is excluded. The occurrence of PME

and squalane indicates a contribution of archaebac-

teria to the organic matter (Holzer et al., 1979;

Risatti et al., 1984), although both compounds were

also suggested to be derived from algal sources

(Kenig et al., 1995). Lycopane, abundant in most

samples, is generally attributed to algal sources

(Kohnen et al., 1993; Salmon et al., 1997). Diage-

netic degradation products of chlorophyll derived

phytol including phytane, pristane, norpristane and

i-C16 occur in all samples and except for the lime-

stones (K, KW) in high abundances. A dominance

of phytane over pristane and shorter chain com-

pounds is always found, with pristane/phytane-

ratios ranging between 0.2 to 0.9. Although the

pristane/phytane-ratios do not strictly follow litho-

facies types, lower values of 0.2 to 0.5 were

observed for the laminated marls and the chert

layers. Limestones generally reveal higher pristane/

phytane-ratios of 0.5 to 0.9 whereas marls and sili-

ci®ed marls show a wide distribution of pristane/

phytane-ratios. No depth trend was recognized for

this ratio and thus the high variability for this par-

ameter re¯ects rapid ¯uctuations in the depositional

conditions of the Malm z. Because terrigenous in¯u-

ences can be ruled out, changes are due to vari-

ations of sealevel and associated biological input,

salinity and redox potential in the intra-reefal set-

ting. The extremely low pristane/phytane ratios of

the laminated marls argue for strictly anoxic con-

ditions during sedimentation (Brooks et al., 1969;

Didyk et al., 1978) possibly coupled to higher sali-

nities. Low pristane/phytane-values were recognized

in a variety of enhanced salinity environments (Hite

et al., 1984; ten Haven et al., 1985, 1988; Schwark

and PuÈ ttmann, 1989; de Leeuw and Sinninghe

DamsteÂ , 1990; Kenig et al., 1995). In hypersaline

environments halotolerant bacteria containing high

contents of phytanyl lipids (Albrecht et al., 1976)

can be very abundant and thus a low pristane/phy-

tane ratio in special environments may be re¯ecting

the salinity depended growth rate of bacteria rather

than the degree of anoxicity (de Leeuw and Sin-

ninghe DamsteÂ , 1990).

The ratios of pristane/n-C17 and phytane/n-C18

also do not show a distinctive facies control but

reveal a general trend towards higher values around

110 m depth, i.e. in the center of the Malm z 2

interval. Plotted in a pr/n-C17 vs. ph/n-C18-diagram

(Shanmugam, 1985; Talukdar et al., 1993) all except

the white limestone values fall in the range of mar-

ine algal derived organic matter deposited under

strongly reducing conditions. This diagram groups

laminated marl and chert samples at more reducing

and non-laminated marls and limestones at less

reducing conditions.

Hopanes and hopenes. A C27 to C35 series of

hopanes and hop(17,21)enes dominates in all but

the KW samples (Fig. 6), indicating an eubacterial

and/or cyanobacterial input (Ourisson and

Albrecht, 1992; Rohmer et al., 1992; Ourisson et

al., 1994). Both series posses the 17a(H),21b(H)

con®guration and extended C31 to C35 members

occur as doublets of 22S and 22R isomers (Fig. 6).


Besides the two dominating hopanoid types, more-

tanes occur in the C27 to C31 range and neohop-

(13,18)ene accompanied by 30nor-neohop(13,18)eneis present in most samples.

The relative amounts of hopenes to hopanes is

fairly constant for the laminated marls (2.0 to 2.5)and more variable for the non-laminated marls (0.8

to 4.5) with a tendency to higher values above

110m depth. Data frequency for limestones and sili-

ci®ed marls (K, KM) is insu�cient for interpret-ation and only trace amounts of hopanoids occur in

KK and KW samples.

The high abundance of unsaturated hopenes con-

®rms a low level of maturity and has been noted

for a variety of hypersaline environments (Boonet al., 1983; ten Haven et al., 1985, 1988; Kohnen

et al., 1991; de las Heras et al., 1997). The low

maturity is in accordance with petrological results(Vliex and Schwark, 1998). In contrast, the degree

of isomerisation at the C22 position of the

hop(17,21)enes has already reached equilibrium

values of (22S/(22S+22R))=0.50±0.53. Accordingto Sinninghe DamsteÂ et al. (1995) the isomerisation

for homohop(17,21)enes reaches an end point at

0.52±0.53 for the 22S/(22S+22R) ratio. This anda C27 a/(a+b) ratio of 0.80±0.82 would either

correspond to higher level of maturity or point

towards a speci®c depositional environment and

diagenetic history.

Comparable distributions of C31 to C35-

hop(17,21)enes and hopanes showing similar con-

versions rates at C22 were identi®ed by Boon et al.(1983), ten Haven et al. (1985, 1988) and Kohnen et

al. (1991) in hypersaline environments. Ten Haven

et al. (1985, 1988) concluded that in hypersaline en-vironments hopanes were formed from hopenes by

direct reduction rather than by isomerisation of the

unstable 17b(H),21b(H)hopanes and regard this

speci®c pattern as characteristic for an enhancedsalinity environment.

The distribution pattern of the C31 to C35

analogues provides further arguments for high

reduction potential and salinity in the palaeo-

depositional environment during sedimentation ofthe marls due to high abundance of the extended

hop(17,21)enes. Sample ML2 is exceptional for con-

taining no hopenes and samples ML5 and ML125show only trace amounts. Despite of this, a clear

di�erentiation between laminated and non-lami-

nated marls can be achieved by extended hopene

distribution (Fig. 6). Laminated marls show a moresymmetrical distribution with a maximum at the

C34-hopenes whereas non-laminated marls systema-

tically show a decrease from C31 to C32 membersfollowed by maximum at C33 and then a constant

decline of the C34 and C35 members. Silici®ed marls

reveal an extended hopene distribution maximising

at C31 and then smoothly declining to the C35

Fig. 6. Mass fragmentograms of m/z= 191 and 367 showing distribution of hopanes and hopenes forthree lithofacies types marls, silici®ed carbonates and laminated marls. Numbers indicate numbers ofcarbon atoms. Filled triangles represent hop(17,21)enes, stars denote neohop(13,18)enes, open circles in-

dicate moretanes and ®lled circles ab-hopanes.


member (Fig. 6). Pure limestones and cherts do not

contain hopenes.

Steranes and sterenes. The saturated and unsatu-

rated steroids consist of C27 to C29 compounds with

only traces of C30 and no C26 components (Fig. 7).

Diasterenes are missing in the samples as character-

istic for many clay-depleted carbonatic environ-

ments. However, D13(17)-spirosterenes (Fig. 8) occur

in signi®cant amounts and monoaromatic des-

methyl- and methylsteranes are major and often the

dominating members of aromatic fractions. Due to

the low maturity and possibly due to the low

amount of clay mineral catalysts, the steroid distri-

bution is dominated by instable intermediate pro-

ducts of steroid diagenesis. Unusual distributions of

steroids were encountered that are related to vari-

ations in (i) biological input into an environment

stressed by high salinity and anoxia or (ii) the early

diagenetic conditions. These will be in¯uenced by

the special mineralogy of the sediments and possibly

by exceptional microbial mediation pathways of

early diagenetic reactions.

The distribution pattern of the saturated steranes

is strongly a�ected by these in¯uences and reveals

an unusual pattern of aaa- and abb-steranes (Fig. 7),with diagenetically intermediate baa-steranes miss-

ing, except for traces of the C27baa-sterane. The

aaa-steranes are dominated by C27- and C29-com-

pounds (40±50% and 35±45%, respectively) with

C28-steranes comprising only 10±15%. The abb-steranes are composed of lower amounts of C27-

and C29 steranes (25±30%) but contain up to 50%

C28-steranes. Consistent with the low maturity of the

bitumens, the ratio of aaa/abb-steranes is very high

for cholestane and ethylcholestane. Accordingly, the

ratio of 20S to 20R isomers of those compounds is

particularly low, with 20S-members often missing.

The methylcholestanes, on the contrary, show a

pronounced dominance of the abb- over aaa-ster-anes (Fig. 7). This deviation can not be related to

an increased thermal maturity exclusively for the

methylcholestanes (e.g. due to impregnation with

more mature migrated bitumens) but rather re¯ects

a speci®c input, possibly from D7-sterenes (de

Leeuw and Sinninghe DamsteÂ , 1990) via intermedi-

ate formation of D13(17)-spirosterenes (Peakman et

al., 1989).

These labile compounds occur with large vari-

ations of the 4 most prominent isomers 5b20R-,5b20S-, 5a20R and 5a20S-D13(17)-spirosterenes

(Fig. 8). For C27-members, a ratio of 0.8 was deter-

mined for the relative abundance of 5b/5a-isomers

(based on intensities in m/z = 206 mass fragmento-

grams). The C28-compounds give a 5b/5a-isomer

ratio of 5.0, whereas the C29-spirosterenes again

reveal a 5b/5a-isomer ratio of only 0.4 (Fig. 8). The

diagenesis of spirosteroids must have proceeded

di�erently for the C28-member as compared to the

C27- and C29-compounds and most likely was

triggered by variable contributions from a speci®c

precursor sterol.

The sterene distribution con®rms the observation,

that C27- and C29-steroids show similarities but dif-

fer strongly from C28-steroids. No regular sterenes

and only trace amounts of diasterenes were detected

in the samples but a series of compounds eluting

prior to the regular steranes occurs in signi®cant

abundance (Fig. 8). These were tentatively identi®ed

as C27 to C30-sterenes by mass spectra [Fig. 9(a)].

The mechanism of formation for these sterenes is

not clear and an origin from other precursors, e.g.

norlanostenes might not be excluded but is not in

agreement with the C27 to C29 distribution pattern.

Four isomers occur for each sterene, all compounds

characterized by a strong M+-43 ion, indicating

loss of an isopropyl-group and a strong signal at

M+-56 giving ions of m/z = 314, 328 and 342,

respectively [Fig. 9(a)].

The compound distribution for this steroid

type is C29>C28>C27>>C30 and thus di�ers

markedly from those of saturated steranes

Fig. 7. Distribution of steranes and sterenes exemplarilyshown for sample M110 as given by mass fragmentogramsof m/z = 217, 218 and 215. Numbers indicate total num-ber of carbon atoms per molecule. Triangles representsterenes, star indicates baa-cholestane, ®lled and opensquares denote abb-steranes with 20R and 20S con®gur-ation and ®lled and open circles indicate aaa-steranes with

20S and 20R con®guration, respectively.


Fig.8.(a)Mass

fragmentogramsofm/z

=206,220and234indicate

distributionofC27to

C29spiro(13,17)enes.Open

circlesandsquaresindicate

5b-isomerswith20S

and20R

con®guration

and

®lled

circlesandsquaresindicate

5a-isomerswith

20S

and20R

con®guration,respectively.Shaded

peaksin

them/z

=234-fragmentogram

depictdialkylthiophenes.(b)Mass

fragmentogramsofm/z

=370,384,398indicatingaseries

ofunknownC27to

C29sterenes,each

comprising4isomersthatelute

shortly

after

thespirosterenes.TheC27andC29mem

bersshow

similarisomer

distributionpatterns,whereastheC28analogues

displayadi�erentisomer

distribution.Mass

spectra

ofcompoundsare

shownin

Fig.9(a).(c)Mass

fragmentogramsofm/z

=368,382,396.Thesterenes

shownin

(b)are

accompaniedbyaseries

ofunknownsteradienes

elutingin

thearomaticfraction.Theoccurrence

ofthesecompoundswaspreviouslyreported

fortheOrbanouxsite

byvanKaam-PetersandSinningheDamsteÂ(1997).

Correspondingmass

spectraare

shownin

Fig.9(b).


(C27rC29>>C28>>C30). As already noted for thespirosterenes and regular steranes, the C27- and C29-compound show a similar distribution of isomers

that is quite distinguishable from those of the C28-members [Fig. 8(b)]. Therefore, although the precisestructure of the modi®ed sterenes has still to be

fully elucidated, the biological precursors of theC28-steroids must be di�erent from those of theC27- and C29-members and consequently undergo a

di�erent diagenesis route.Because of low thermal maturity of Malm z bitu-

mens, deviations in early diagenesis pathways mustaccount for the irregular isomer pattern of satu-

rated steranes. Enhancement in the abundance ofabb-steranes has been previously observed in hyper-saline environments (ten Haven et al., 1985, 1988;

de Leeuw and Sinninghe DamsteÂ , 1990) and a poss-ible input of D7-sterols was proposed by Peakmanet al. (1989) and de Leeuw and Sinninghe DamsteÂ

(1990). In the case of the Malm carbonates sucha sterol input seems likely and this diageneticroute is supported by the concomitant occurrence

of spirosterenes. Furthermore, the similar isomerdistribution pattern of the unknown sterenes andthe spirosterenes might indicate a microbial me-

diation that preferentially a�ects the C28-memberdue to its biological inheritance of the double bondposition.

A marine origin has to be encountered forall steroids because due to the absence of otherterrestrially derived biomarkers and microscopicalobservations the terrigenous input for this deposi-

tional setting was extremely low. A large varietyof C28-sterols is produced by autotrophic plank-tonic organisms (Scheuer, 1978; Volkman, 1986,

1988) that will allow for di�erent precursors anddiagenetic routes as compared to C27- and C29-steranes.

Fig. 9. (a) Mass spectra of unknown sterenes shown in Fig. 8(b). Mass spectra were recorded from thehighest peak, i.e. the third eluting isomer. (b) Mass spectra of unknown steradienes shown in Fig. 8(c).

Mass spectra are shown for the ®rst eluting isomer.


Aromatic fractions

Aromatic fractions of Malm z carbonates o�er a

spectrum of components that is dictated by lowmaturity and high availability of reduced sulfur

species. Due to the low thermal maturity and thelack of terrigenic input, naphthalenes, phenan-

threnes, dibenzothiophenes, ¯uorenes, biphenyles

and their alkylated homologues are found only intrace amounts.

As a result the aromatic fraction is mainly com-

posed of aromatic steroids, benzohopanes, alkyl-chromans, perylene, an aromatized triterpenoid and

minor amounts of alkylbenzenes. In the intra-reefal

iron-limited depositional environment sulfur incor-poration into functionalized lipids (Sinninghe

DamsteÂ et al., 1990) occurred frequently and severalseries of organic sulfur compounds are present

including various acyclic thiophenes and thienylho-panes. No sulfur bearing steroids or carotenoids

were detected.

Benzohopanes are typical constituents of carbona-

tic depositional environments and are suggested tobe formed by cyclisation of bacterial C35-hopanoids

during very early stages of diagenesis (Hussler etal., 1984; Wei and Songnian, 1990; Schae�er, 1993).

These compounds occur ubiquitously and do not

o�er much potential for environmental characteriz-ation. In signi®cant abundances a B-ring monoaro-

matic triterpenoid of the fernane/arborane type(Hauke et al., 1992) occurs in all samples. A mi-

crobial as well as an angiospermal origin for the

arborene/fernene precursor is possible (Hauke et al.,1992, 1995) but due to the widespread occurrence in

pre-Cretaceous sediments a bacterial or even algalsource has been postulated for these compounds.

This bacterial input also has to be encountered forthe Malm z samples which predate the evolution of

angiosperms. None of the A-ring degraded or dia-

romatic analogues often co-occurring with themonoaromatic pentacyclic triterpenoid were

detected and no further paleoenvironmental infor-mation can be derived from the occurrence of the

ferna/arboratriene.

Steroids. Monoaromatic desmethyl and 4-methyl-steroids occur in large concentrations in the Malm

samples and often comprise the most abundantcompounds in the aromatic fraction. The C27 to C29

desmethyl monoaromatic steroid distribution shows

no contribution of rearranged steroids comparableto the lack of diasterenes in the aliphatic fraction.

Due to co-elution of the C28abR- with the C29bbR-isomer a precise calculation of the relative contri-

butions is hindered but the ethylcholestanes always

dominate the monoaromatic steroid distributionpattern. On average a distribution of 30:45:25 for

the C27:C28:C29 monoaromatic steroids occurs,which is directly opposite to the one observed for

the saturated steroids. Biological input estimation

based on steroid distribution following the ternary

discrimination plot of Huang and Meinschein

(1979), as often applied in paleoenvironment assess-

ment (Peters and Moldowan, 1993), will thus give

highly unreliable results.

The ratio of desmethyl- vs. 4-methyl-monoaro-

matic steroids varies between 1.3 and 2.8. The high

amount of 4-methyl-monoaromatic steroids indi-

cates a major production of organic matter by mar-

ine algae, including those from microscopically

identi®ed dino¯agellates, in the Rennertshofen

Trough.

A series of C26 to C29-steradienes was detected in

the aromatic fraction [Fig. 8(c)], which was pre-

viously reported by van Kaam-Peters and Sinninghe

DamsteÂ (1997) for the Jurassic Carbonates at

Orbanoux. The structures of these compounds are

still unknown and the mass spectra exhibit a strong

similarity with those of the unknown sterenes found

in the aliphatic fraction [Fig. 9(c)]. The distribution

pattern shows no clear relationship to any of the

other steroid classes.

Three C27 to C29-compounds occuring in the aro-

matic fraction were tentatively identi®ed as posses-

sing a diaromatic steroid skeleton based on the

occurrence of a m/z= 249 mass fragment and mol-

ecular ions reduced by 4 Da as compared to mono-

aromatic steroids. A/B diaromatic steroids were

tentatively identi®ed in Monterey Formation by de

Lemos Sco®eld (1990) and di�erent MS±MS exper-

iments as well as chemical ionisation was carried

out on these components. However, the mass spec-

tra (EI, 70 eV) of those diaromatic steroids do not

fully match with those from the Malm samples and

therefore a related, e.g. anthrasteroidal or regular

vs. rearranged, structure has to be assumed. The

distribution of the diaromatic steroids shows a clear

dominance of the C27 and C29 compounds, whereas

the diaromatic methyl cholestane occurs in modest

amounts only. This pattern is comparable to the

one of the saturated steranes and opposite to that

of the monoaromatic steroids. This indicates a

further complication of the diagenetic history of

steroids in the Malm samples from the

Rennertshofen Trough. Palaeoenvironmental assess-

ment based on one of the standard saturated or

monoaromatic steroid composition parameters can

not provide a representative picture of biological

input and early diagenetic conditions (Figs 7, 8 and

10).

Perylene. The most prominent fully aromatized

constituent of the aromatic fractions is perylene, a

compound that frequently occurs in marine and

lacustrine environments, even if other PAH-

compounds are missing and therefore a combustion

origin is excluded. Aizenshtat (1973), La¯amme

and Hites (1978), Gschwend et al. (1983) and

Louda and Baker (1984) suggested, that perylene

may be directly derived from biogenic precursors.

Aizenshtat (1973) described that the reduction of


chinone pigments would produce perylenes. These

pigments have been found in insects (Cameron et

al., 1964), fungi (Thompson, 1979) but also in leafs

of terrestrial plants (Orr and Grady, 1967). Because

chinone pigments are sensitive to oxidation, a for-

mation of perylene under anoxic condition was pro-

posed (Orr and Grady, 1967; Wakeham et al., 1979;

Louda and Baker, 1984). However, chinone pig-

ments with a perylene skeleton are not abundant in

nature and there is a contrast between pigment con-

centration and abundance of perylene of sediments

(Watts and Maxwell, 1977). Wakeham et al. (1979)

proposed that precursors of perylene are not necess-

arily of terrestrial origin, because the occurrence of

high amounts of perylene in marine sediments (Orr

and Grady, 1967; La¯amme and Hites, 1978; Wake-

ham et al., 1979; Louda and Baker, 1984; Venkate-

san, 1988).

In case of the Malm z carbonates a terrestrial ori-

gin of perylene is not likely, because of a lack of

other terrestrial biomarkers. A marine precursor, as

suggested by Wakeham et al. (1979) could be an

Fig. 10. In addition to the steradienes shown in Figs 8 and 9 and the dominating monoaromatic ster-oids (accompanied by traces of triaromatic steroids), the aromatic fractions of the Malm z samplesreveal the presence of tentatively identi®ed diaromatic steroids as shown by a) the mass fragmentogramof base peaks m/z = 210. Mass spectra recorded for the C27 and C29 diaromatic steroids are shown in

(b) and (c), respectively.


alternative explanation for the high concentration.

Louda and Baker (1984) proposed sul®de sensitive

marine microbes or algae (diatoms, which are unli-

kely for Malm z samples) as possible precursors.

This explanation would be in accordance with the

facies conditions of Malmian samples, where main

producers of organic matter are algae or bacteria. It

is generally accepted that high abundances of pery-

lene are associated with strictly anoxic conditions

(Venkatesan, 1988; Peters and Moldowan, 1993)

although the potential biogenic origin and the diag-

entic route for perylene formation are still not unra-

velled (Silliman et al., 1997).

Chromans. Four alkylated 2-methyltrimethyltride-

cylchromans (MTTCs) were detected in Malm zsamples by ion chromatograms of m/z =

121 + 135 + 149. These compounds were ®rst dis-

covered in sediments and crude oils by Sinninghe

DamsteÂ et al. (1987a) and it was proposed that

MTTCs are directly biosynthesised because of their

limited numbers of potential isomers. Widespread

tocopheroles, although structurally closely related

to chromans, were excluded to be precursors of

MTTCs. Although biological precursors for

MTTCs could not be identi®ed until today, based

on compound speci®c carbon isotope data, an ori-

gin from eu- or archaebacteria has been proposed

(de Leeuw and Sinninghe DamsteÂ , 1990; Sinninghe-

DamsteÂ et al., 1993; Kenig et al., 1995). An alterna-

tive formation of chromans via condensation of al-

kylated phenols with phytol was postulated by Li et

al. (1995) and the generation mechanism of MTTCs

is still under debate (Li and Larter, 1995; Sinninghe

DamsteÂ and de Leeuw, 1995).

Based on empirical observations it was suggested

that in sediments from non-hypersaline environ-

ments 5,7,8-trimethyl-MTTC dominates and 8-

methyl-MTTC is completely missing. For the inves-

tigated samples 5,7,8-trimethyl-MTTC is the most

prominent compound, but 8-methyl-MTTC also

occurs, which infers enhancement of salinity but no

severe hypersalinity (i.e. >120-). Similar obser-

vations were made for the Permian Kupferschiefer

(Schwark and PuÈ ttmann, 1989; Grice et al., 1997) in

agreement with slightly enhanced ``mesosaline'' con-

ditions. Mesosaline refers to a salinity between 40

and approximately 120-, i.e. before onset of gyp-

sum precipitation at 140- (Kirkland and Evans,

1981). For a more elaborated characterisation of

palaeosalinities the MTTC ratio was de®ned by

Sinninghe DamsteÂ et al. (1989); Sinninghe-DamsteÂ

et al. (1993) as: MTTC-ratio = 5,7,8-trimethyl-

MTTC/total MTTCs. For the Malm z sediments

investigated here, the ratio was calculated to vary

from 0.55±0.61, indicating no signi®cant changes in

palaeosalinity.

In Fig. 11 MTTC-values are plotted against the

pristane/phytane-ratio. This plot was established to

discriminate a ``normal'' marine from hypersaline

environments (Sinninghe DamsteÂ et al., 1989).

Hypersaline conditions are characterised by pris-tane/phytane values <0.2 and MTTC-values <0.5,

whereas a ``normal'' marine environment is marked

by pristane/phytane-ratios of >0.3 and MTTC-values >0.6. All Malm samples plot in the ®eld of

``normal'' marine or beginning ``mesosaline'' con-

ditions but ``hypersaline'' conditions are not

reached. This would argue for normal marine tomoderately increased salinity within the photic zone

of the water column, where these compounds are

assumed to be produced.OSC (organic sulfur compounds). Organic sulfur

compounds (OSC) occur as free molecules in

extracts of sediments, but can also be bound to the

high molecular weight fraction (Sinninghe DamsteÂ

et al., 1990; Kohnen et al., 1993). They are typical

constituents of highly reducing conditions (e.g. de

Leeuw and Sinninghe DamsteÂ , 1990; Schae�er etal., 1995) and are formed by a direct incorporation

of reduced sulfur species into functionalized lipids

during early diagenesis. The formation of organicsulfur compounds occurs either near the sediment

water interface (Orr and Sinninghe DamsteÂ , 1990)

or at shallow depth in sediment. An alternative bio-

synthetic origin was proposed for selected bicyclicand tetracyclic terpenoid and hopanoid sulfur com-

pounds by Cyr et al. (1986). Payzant et al. (1986)

proposed that such compounds may be accessoryphotosynthetic pigments. It is now generally

accepted that OSC are products of early diagenetic

sulfur incorporation and that speci®c structural fea-

tures inherited from reaction with the functionalized

Fig. 11. Crossplot of MTTC-ratio vs. pristane/phytane-ratio with indications of data ®elds for normal marine and

hypersaline environments.


lipids are preserved in the OSC structures thus

allowing to reconstruct original biological input

(Kohnen et al., 1993). The free OSC occuring in the

``aromatic'' fractions were identi®ed based on com-

parison of mass spectra and ion chromatograms

with reference spectra in the literature.

Thienyl hopanes. The C35-thienyl hopane isomers

17a(H),21b(H), 17b(H),21a(H) and 17b(H),21b(H)

commonly found in sulfur-rich environments (Vali-

solalao et al., 1984) were identi®ed in all samples

investigated. It was suggested that these hopanes

derive directly from sulfur incorporation into bac-

teriohopanetetrol, the reason for high C35-concen-

tration being a spontaneous reaction of the alcohol

with reduced sulfur. This reaction occurs at early

stages of diagenesis in strongly anoxic environments

preventing biotransformation or mineralisation (de

Leeuw and Sinninghe DamsteÂ , 1990). High concen-

trations of thienyl- and benzohopanes indicate an

intensive reworking of organic matter or a deri-

vation of hopanoids from cyanobacteria (Schae�er

et al., 1995).

The occurence of C35-thienyl-hopanes is in agree-

ment with the dominance of extended hop(17,21)-

enes in the aliphatic fraction. Ten Haven et al.

(1985, 1988) reported, that in many samples re¯ect-

ing high saline environments extended C35-members

preferentially occur. High amounts of benzo- and

thienylhopanes together with the increased abun-

dance of C35-hopanes indicate strongly reducing

conditions and may also point towards a higher

saline environment.

Alkylthiophenes. Incorporation of sulfur in unsa-

turated aliphatic precursors produces substituted

thiophenes including 2-alkylthiophenes, 2-alkyl-5-

methylthiophenes, 2-alkyl-5-ethylthiophenes, various

mid chain 2,5- and 3,4-dialkylthiophenes and mono-

methyl-thiophenes (Sinninghe DamsteÂ et al., 1986,

1987a, 1989, 1990; Peakman and Kock-van Dalen,

1990; Kohnen et al., 1991, 1993; Russell et al.,

1997, de las Heras et al., 1997). Except for the long-

chain 3,4-dialkylthiophenes all compound classes

are present in the Malm samples investigated.

Inspection of the m/z = 111 mass fragmentogram

shows 2-alkyl-5-methylthiophenes (referred to as

MATP) with the n-alkyl side chain ranging from C9

to C27 dominating in all samples (Fig. 12). A trimo-

dal distribution is observed in most samples, the

®rst maximum occuring at the C18-, the second at

the C21- and the third at C24- or C26-MATP.

Di�erences in chain length distribution can be used

to group samples into two classes of long chain

dominated (LC-MATP) and short chain (SC-

MATP) methyl-alkylthiopenes. Samples ML26 and

ML 80 represent SC-MATP, whereas samples

ML69 and ML71 belong to the LC-MATP group

with sample ML67 taking an intermediate position.

The nonlaminated marls can be subgrouped accord-

ingly with samples M102, M104 and M106 repre-

senting SC-MATP, samples M52, M110, M112,

M118 representing LC-MATP and samples M30

and M77 showing equally distributed MATP.

Intervals of similar chain length distribution over

the studied core section seem to be indicated but

the current database does not allow for further in-

terpretations due to the high variability of sedi-

ments and organic fractions. Presently, it can only

be speculated that the controls on chain length dis-

tribution of the MATP may be related to the degree

of sulfurization and thus the proximity of the che-

mocline to the bioproductive photic zone (e.g.

Kenig et al., 1995). The distribution pattern of

MATP can however be shown to be largely inde-

pendent from lithofacies type. Although lower

amounts of MATP were found in the non-marly

lithologies, the K samples show comparable distri-

butions and MK also show identical patterns. A

possible explanation might be that after sulfuriza-

tion of lipids had already proceeded, a sili®cation

of porous carbonate layers occurred, which thus did

not a�ect the MATP distribution. The MATP-pat-

tern shows a slight even predominace in the C18 to

C27 range which is in contrast to n-alkanes charac-

terized by a moderate odd over even predominance

(Fig. 5). Various ``shift'' phenomena between n-

alkanes distribution and patterns of methyl-, ethyl-

and propyl-substituted n-alkyl-thiophenes were

recognised by Sinninghe DamsteÂ et al. (1986) but a

satisfying explanation for the di�erent behaviour of

alkylthiophenes is still missing.

The characteristic low CPI-values of the free n-

alkanes with special preference of the C22 and C24

members observed in other enhanced salinity en-

vironments (ten Haven et al., 1985, 1988; Barbe et

al., 1990), might be obscured by the preferential sul-

furization of these compounds and thus their occur-

ence as MATP. Upon release of these compounds

from the thiophene fraction the expected hypersa-

line n-alkane distribution will be generated. A selec-

tive incorporation of the C22-precursor into the

kerogen matrix is unlikely due to the free occurence

of these compound in other settings (Barbe et al.,

1990).

Non-substituted and ethyl- or propyl-substituted

alkylthiophenes occur in minor concentrations as

revealed by inspection of m/z = 97, 125 and 139

mass chromatograms. Due to comparably low

abundance and and multiple isomers for the substi-

tuted series those compounds are not further dis-

cussed here.

A second series of 2,5-di-n-alkylthiophenes or

midchain dialkylthiophenes (referred to as DATP)

is very prominent in the higher molecular weight

region (Fig. 12). The peaks labelled w in Fig. 12

comprise a series of three DATP-isomers per peak.

The C27-compound mixture for example consists of

three isomers possessing a n-C9/n-C14-, n-C10/n-C13-

and n-C11/n-C12-di-n-alkylsubstitution pattern. A


distribution starting with three coeluting C20-iso-

mers: n-C6/n-C10-, n-C7/n-C9- and n-C8/n-C8-di-n-

alkylthiopene continues to C29 by addition of one

acetyl-group alternatingly to both side chains.

The DATP distribution extends from C22 to C30

in most samples and is characterized by a strong

preference of the C26- followed by the C24 com-

pound. The pattern reveals a strong predominance

of the even-numbered homologues with OEP-values

of 0.55 to 0.95 in the C23- to C28-DATP range. No

dependence of OEP-values calculated from DATP-

distributions with lithology was observed. This

again demonstrates that organic matter input and

early diagenesis was not primarily controlled by

Fig. 12. Mass fragmentograms of m/z= 111 indicative for alkylthiophenes plotted for three samples ofthe marl lithofacies type. Numbers indicate total numbers of carbon atoms per molecule. Filled circlesdenote 2-methyl-5-alkylthiophenes, open circles indicate dialkylthiophenes occurring as mixtures of

three di�erent isomers (see text).


lithofacies and that organic matter distribution will

provide additional palaeoenvironmental infor-

mation.

Isoprenoid thiophenes. Various isoprenoid thio-

phenes and benzothiopenes were found in all

samples of the Malm z sediments. Isoprenoid

bithiophenes also characteristic of other enhanced

salinity environments (Sinninghe DamsteÂ et al.,

1990; Kohnen et al., 1993; de las Heras et al., 1997;

Russell et al., 1997) were not detected in this sample

set and the frequently occuring thiophenes of the

highly branched C20- and C25-isoprenoid type

(HBI) also were not found in the Malm z samples.

These compounds usually occur in the ``free'' form

and their lack in the thiophene fraction is consistent

with the absence of HBIs in the aliphatic fractions.

Cyclisation of precursor molecules can produce var-

ious alkylated benzothiophenes, of which the series

of the mono- and dimethylated alkylbenzothio-

phenes were found in the Malm z samples in higher

abundance. The overall distribution pattern was not

further studied and not used in palaeoenvironmen-

tal assessment.

Instead it was preferred to exclusively investigate

the C19 and C20 thiophene compounds by inspecting

the m/z = 294 and 308 mass fragmentograms

(Fig. 13). This provides information about the dis-

tribution of isoprenoidal thiophenes originating

from C20 functionalized lipids and allows to resolve

questions of biological input and salinity.

Isoprenoid benzothiophenes occur as C16 to C20

pseudo-homologues and are dominated by the C16

and C20 compounds reported from several environ-

ments (Sinninghe DamsteÂ et al., 1987b). The C20

isoprenoid thiolanes occur in trace amounts in

lithographic limestone. These compounds were

reported by Sinninghe DamsteÂ et al. (1986, 1987b)

and re¯ect an intermediate structure in formation

of corresponding thiophenes. Isoprenoid thiophenes

were found to be more prominent than thiolanes

Fig. 13. (a) Mass fragmentogram of m/z = 294 showing distribution of C19 thiophenes. Peak labelling:®lled diamonds denote 1, 2-butyl-5-(1-methyldecyl)-thiophene; 2, 2,5-diheptyl-3-methylthiophene; 3, 2-methyl-5-(4-methyltridecyl)-thiophene; open circles denote 1, 2-heptyl-5-octylthiophene; 2, 2-hexyl-5-nonylthiophene; 3, 2-pentyl-5-decylthiophene; 4, 2-butyl-5-undecylthiophene; 5, 2-propyl-5-dodecylthio-phene; 6, 2-ethyl-5-tridecylthiophene; 7, 2-methyl-5-tetradecylthiophene; peak labelled with star basedon its mass spectrum was tentatively identi®ed as 3-methyl-4-tetradecylthiophene. (b) Mass fragmento-gram of m/z= 308 showing distribution of C20 thiophenes. Peak labelling: ®lled triangles denote isopre-noid-thiophenes: 1, 4-(4,8-dimethylnonyl)-2-(2-methylbutyl)thiophene; 2, 5-(2,6-dimethylheptyl)-2-(3-methylbutyl)-3-methylthiophene; 3, 5-(3,7-dimethyloctyl)-2-(2-methylpropyl)-4-methylthiophene; 4, 5-(2,6-dimethyloctyl)-2-(3-methylbutyl)-3-methylthiophene; 5, 5-(2,6,10-trimethyltridecyl)-2,3-dimetylthio-phene; 6, 2-(3,7,11-trimethyldodecyl)-3-methylthiophene; open cirles denote dialkylthiophenes: 1, mix-ture of 2-heptyl-5-nonylthiophene and 2-hexyl-5-decylthiophene; 2, 2-pentyl-5-undecylthiophene; 3, 2-butyl-5-dodecylthiophene; 4, 2-propyl-5-tridecylthiophene; 5, 2-ethyl-5-tetradecylthiophene; 6, 2-methyl-

5-pentadecylthiophene.


and isoprenoidal benzothiophenes in the Malm zsamples. Isoprenoid thiophenes have been reported

from oils and sediments from a variety of environ-

ments by Brassell et al. (1986), Sinninghe DamsteÂ et

al. (1986, 1987b, 1989, 1990); Orr and Sinninghe

DamsteÂ (1990); Peakman and Kock-van Dalen

(1990); Kohnen et al. (1993) and Russell et al.

(1997). Most prominent isoprenoid thiophenes are

the C20 homologues, which show a characteristic

pattern in the m/z = 308 ion chromatogram. After

Orr and Sinninghe DamsteÂ (1990) the structure of

C20 isoprenoids strongly suggests an origin from in-

corporation of reduced inorganic sulfur into phytol

and/or archeobacterial phytenes or their diagenetic

products. Sulfurisations reactions of phytenic acid

and phytenol take place in sediments (Kohnen et

al., 1993). C20 isoprenoid thiophenes occur in sedi-

ments of ``normal'' marine to ``hypersaline'' en-

vironments in varying concentrations and were

therefore introduced as indicators for palaeosalinity

(Sinninghe DamsteÂ et al., 1989; Kohnen et al.,

1990; de Leeuw and Sinninghe DamsteÂ , 1990).

In Fig. 13 the ion chromatograms of m/z = 294

and 308 illustrate the distribution of C19 and C20

thiophenes. Terminal isoprenoid thiophenes V, VI

and mid chain thiophene isoprenoids I±IV accord-

ing to the notation used by de Leeuw and

Sinninghe DamsteÂ (1990) and Kohnen et al. (1990)

for calculations of the isoprenoid thiophene ratio

ITR, are identi®ed in the m/z= 308 fragmentogram

by comparison with published mass spectra and

retention times (Sinninghe DamsteÂ et al., 1986,

1987a, 1989). In addition to the commonly found 2-

methyl-5-pentadecyl- and 2-ethyl-5-tetradecylthio-

phenes two chromatographically resolved di-n-

alkylthiophenes occur (2-propyl-5-tridecyl- and 2-

butyl-5-dodecylthiophene) and the m/z = 308 mass

fragmentogram shows a further peak containing a

mixture of 2-octyl-5-nonyl-, 2-heptyl-5-decyl- and 2-

hexyl-5-undecyl-thiophenes. HBI-thiophenes as

mentioned above are missing. The C19 compound

distribution as illustrated by the m/z = 294 mass

chromatogram is devoid of any isoprenoid thio-

phenes (Fig. 13) but in addition to a series of 2,5-

dialkylthiophenes three methyl-branched thiophenes

are present (Fig. 13). These branched thiophenes

most probably originate from 9-methyl-nonadeca-

diene precursors (Sinninghe DamsteÂ et al., 1989)

and thus provide evidence for a speci®c microbial

input, probably from sulfur bacteria (Sinninghe

DamsteÂ et al., 1989).

Isoprenoid thiophene V is the most prominent

constituent of the C20 thiophenes and together with

the C20 isoprenoids possessing a midchain thio-

phene moiety, occurs especially in environments of

enhanced salinity. Isoprenoid thiophene VI occurs

in minor amounts in the Malm samples. In normal

marine environments it usually is accompanied by

the isoprenoid VII carrying the thiophene moiety in

a terminal position. For assessment of palaeosali-

nity the isoprenoid thiophene ratio is calculated as

ITR = (VI + VII)/(I + II + III + IV + V)

according to Sinninghe DamsteÂ et al. (1987b) and

de Leeuw and Sinninghe DamsteÂ (1990).

ITR-values of Malm z sediments are generally

<0.08 pointing towards advanced stages of salinity

enhancement. Indications of such elevated salinities

in the Malmian marls and limestones do not fully

agree with other salinity-indicators like pristane/

phytane- or MTTC-ratio. The correlation crossplot

of ITR with the pristane/phytane- and MTTC-ratio

is given in Fig. 14 and 15. The pristane/phytane-

ratio and the ITR seem to be in good agreement,

whereas the MTTC-ratio shows considerable devi-

ation. A similar observation of an underestimation

of palaeosalinities by the MTTC-ratio as compared

to the ITR was made by Schae�er (1993) for the

Messian age Gibellina Marls of Sicily. A consider-

able problem in palaeosalinity assessment occurs

with intensively strati®ed water bodies, possessing

contrasting salinities and/or redox potential. The

MTTC-ratio, if susceptible to salinities via re-

sponses from biological precursor assemblages [see

discussion by Li and Larter (1995), Li et al. (1995)

and Sinninghe DamsteÂ and de Leeuw (1995)] may

re¯ect surface water conditions. The ITR, on the

opposite, might preferentially indicate deep water

or even sedimentary diagenetic conditions although

preservation of carbon skeletons from precursor

Fig. 14. Crossplot of MTTC-ratio vs. ITR, the isoprenoidthiophene ratio as de®ned by Sinninghe DamsteÂ et al.(1989). Open and black-®lled circles indicate laminatedand non-laminated marls, circles ®lled grey represent silici-

®ed lithofacies types.


compounds should still re¯ect responses of biologi-cal communities to salinity variations.

Bound hydrocarbons released by desulfurization ofpolar fractions

One laminated and one nonlaminated marlsample were desulphurized to check whether a sig-

ni®cant bias in the biomarker distribution due toselective sulfur bonding might occur. A drastic biasin the compound distribution could invalidate the

environment characterization based on free bio-marker analysis or at least a�ord a combined in-terpretation of both compound pools.Desulfurization of polar fractions of both samples

a�orded less than 2% of hydrocarbon products andthus the amount of sulfur-bound lipids in the Malmz samples is insigni®cant. No experiments have yet

been carried out to desulfurize the kerogens andthus it is still possible that a considerable pro-portion of labile lipids is still attached to the kero-

gen matrix.Saturated hydrocarbons. The saturated hydrocar-

bons released by Raney nickel desulfurization ofthe polar chromatographic fraction from sample

M110 consist mainly of n-alkanes, steranes andhopanes (Fig. 16). In the case of sample ML69, n-alkanes largely predominate the hydrocarbon distri-

bution, and polycyclic components occur only intrace amounts. The alkane fraction of the latersample is also characterized by the occurrence of an

unresolved complex mixture.

n-Alkanes from sample M110 show a monomodal

distribution and range from C14 to C40 maximising

at C19. A slight odd over even carbon number pre-

dominance can be noted for the components in the

C21±C32 range. For sample ML69, the n-alkane dis-

tribution is monomodal centered around the C17-

and C18-components. A very slight odd over even

carbon number predominance is present is the C27±

C31 range.

In both samples, phytane and pristane are present

in trace amounts. In sample M110, the pristane/

phytane ratio is ca. 0.4, whereas this ratio is close

to 1.2 in sample ML69. This could re¯ect di�er-

ences in the degree of anoxicity between the two

samples with sample M110 more anoxic or just

re¯ect di�erent degrees of sulfurization.

Hopanes are by far more abundant in sample

M110 (Fig. 16). In the later case, the m/z = 191

chromatogram is dominated by gammacerane and

C35 ab-hopane with the 22R con®guration (Fig. 17).

A complete suite of C30- to C35 ab-hopanes is pre-

sent. For this series the 22R components clearly

predominate over the 22S isomers, with 22R/

(22R+ 22S) ratios of ca. 0.64 (C32 and C34 homol-

ogues), 0.56 (C33 component) and 0.84 (C35 homol-

ogues). The high abundance of gammacerane would

be in agreement with the low pristane/phytane-ratio

of the desulfurized polar fraction and indicate depo-

sition under strictly anoxic conditions. Gamma-

cerane has been widely used as an empirical

indicator of palaeosalinity (ten Haven et al., 1985,

1988). Recently it has been postulated that gamma-

cerane originates from bacterivorous ciliates and

might more likely be an indicator of intense water

column strati®cation and possibly a marker for

photic zone anoxia (Sinninghe DamsteÂ et al., 1996).

Salinity strati®cation implies circulation restriction

and possibly temperature strati®cation which in

turn cause an enhancement of redox strati®cation in

the water body. A combination of slightly enhanced

salinity corresponding to the ``mesosaline stage'' and

strictly anoxic conditions is almost inevitable and

gammacerane might be an indicator of coinciding

mesosaline and strictly anoxic conditions. Occur-

rence of gammacerane in non-hypersaline settings

has been reported as well as a lack of gammacerane

in hypersaline settings (ten Haven et al., 1985, 1988;

Sinninghe DamsteÂ et al., 1995b) favoring the view

of a combined salinity/anoxicity e�ect. Gamma-

cerane is the major compound that occurs exclu-

sively in a sulfur-bound mode in the extracts and its

detection in the polar fraction clearly supports the

view derived from the free lipid distribution. In

summary, the m/z = 191 trace of the desulfurized

sample M110 clearly resemble those from organic-

rich marls deposited in a hypersaline context (e.g.

Kenig et al., 1995; Schae�er et al., 1995).

In sample ML69, hopanes occur in trace amounts

only (Fig. 16). The distribution is again predomi-

Fig. 15. Crossplot of ITR, the isoprenoid thiophene ratioas de®ned by Sinninghe DamsteÂ et al. (1989) against thepristane/phytane-ratio. Black-®lled and open circles indi-cate laminated and non-laminated marls, circles ®lled greyrepresent silici®ed lithofacies types. Laminated marls pre-

ferentially plot in the region of enhanced salinity.


nated by the 22R C35 ab-component (Fig. 17). The

main di�erence in sample ML69 consists in the low

relative abundance of gammacerane which is almost

absent. If gammacerane is considered as a marker

for water column strati®cation and possibly photic

zone anoxia (cf. Sinninghe DamsteÂ et al., 1995), this

could re¯ect di�erences between the depositional

environment of the laminated and non-laminated

marls. This would however indicate high anoxicity

and intense strati®cation of the water column for

the non-laminated marl (M110) and more oxic con-

ditions or less marked strati®cation for the lami-

nated marls (ML69). This seems to be in

contradiction with the assumption that laminated

sediments were deposited in a low energy environ-

ment in contrast to sediments where lamination has

been destroyed by water turbulence or benthic

activity. The gammacerane distribution is however

in agreement with the ITR and pristane/phytane-

ratio of the free lipid hydrocarbon fraction that

also indicate higher salinity and anoxicity for the

M110 vs. the M69 sample (Fig. 15).

An interesting feature in sample ML69 is pre-

sence of C30-neohop-12-ene being the predominant

polycyclic component in the alkane fraction. This

compound is also present in sample M110, but in

lower relative abundance. Further investigations

will be aimed towards a closer inspection of the dis-

tribution of that compound in free and bound frac-

tions because currently its palaeoenvironmental

signi®cance remains unclear.

Steranes exclusively occur as baa- and aaa-iso-mers (Fig. 17). In the sterane distribution from

sample M110, the distribution of homologues is

C29>C27>>C28. It is also possible that a C30

sterane occurs in this distribution, but it coelutes

with a C30 methyl sterane. In sample ML69, the

sterane distribution resembles that of sample M110

Fig. 16. GC/MS total ion trace for aliphatic hydrocarbons obtained from desulphurized polar fractionsof a non-laminated (M110) and a laminated marl (ML69). Filled circles represent n-alkanes with num-bers indicate total number of carbon atoms. Open circles and squares denote hopanes and steranes, re-

spectively.


Fig.17.Mass

fragmentogramsofm/z

=191and217shownforthealiphaticfractionofdesulfurizedpolarfractionsofsamplesML69andM110.


(Fig. 17) with a slightly higher relative abundanceof baa- vs. aaa-isomers.

Methylsteranes (presumably 4-methylsteranes) arepresent in both samples (C30>C29>C28), but inmuch lower relative abundance in sample ML69.

Two dinosterane isomers only occur in sampleM110 where they represent the predominant 4-methylsteranes.

The presence of additional ``di''- and ``tri''-meth-ylated steranes indicated by m/z= 245 and 259 asmain fragment in the mass spectra was noted. It

was not determined whether these components rep-resent 3-alkylated steranes (i.e. 3-ethyl- and 3-pro-pyl steranes) or polymethylated components (e.g.2,3-dimethylsteranes or 4,4-dimethylsteranes)

because of low quantities and unknown origin andsigni®cance of theses compounds. Their presence,however, con®rms the highly diverse input of ster-

oidal compounds and the complexity of diageneticproducts observed in the free steroid distribution.Dimethylsteroids could be possible precursors for

the modi®ed sterenes found in the free hydrocar-bons.With both samples, the aromatic fractions of

desulfurized polars consist predominantly of a hugeunresolved complex mixture. With the exception ofalkylbenzenes recorded at m/z = 91, 105 and 133occuring in trace amounts in the C13±C30 range, no

aromatic components could be identi®ed. Due tomultiple coelutions, it was di�cult to obtain massspectra of the alkylbenzenes and therefore proble-

matic to determine if the m/z = 133 componentshave an arylisoprenoid structure. This possibilityseems rather unlikely, as the distributions observed

on the m/z = 133 + 134 mass chromatograms donot show the pattern usually expected for isoprenoi-dal components (i.e. absence or lower abundance ofC12-, C17- and C23-homologues). In addition, no

C40 diarylisoprenoids were observed in the twosamples investigated.

DISCUSSION

In thermally immature, sulfur-rich depositionalsettings, the molecular characterization of free

hydrocarbons and OSC for palaeoenvironmentreconstruction requires the complementary study ofsulfur-bound lipids, if those contribute signi®cantly

to the total extract, in order to avoid any bias fromselective removal of biomarkers from the free hy-drocarbon fractions. Bitumens extracted from theMalm z carbonates in the Rennertshofen Trough,

located in the Franconian Alb, SW-Germany, gaveonly minor quantities of hydrocarbons releasedupon desulfurization with Raney nickel. The com-

position of free hydrocarbons and OSC is thus suit-able for palaeoenvironment characterization.Variations in biomarker distribution between free

and bound lipids provide some additional infor-

mation on biological input, palaeomilieu and dia-

genesis.

The Malmian samples were previously categor-

ized in the three main lithofacies types limestones,

marls and cherts and subdivisions into laminated

and non-laminated marls were made. Biomarker

distribution of aliphatic, aromatic and OSC frac-

tions does not follow the lithofacies development.

Therefore, geochemical results provide signi®cant

additional information on palaeodepositional con-

ditions. The main point of debate in palaeoenviron-

mental assessment of Malm z sediments has been

the characterization of palaeosalinities and in part

of hydrodynamic energy levels, which in turn are

correlated to the redox potential (e.g. Keupp, 1977,

1994; Barthel, 1978; Meyer and Schmidt-Kaler,

1989, 1993; Keupp et al., 1993). One reason being

that hypersaline conditions during deposition would

terminate the growth of sponge and algal reefs on

the carbonate platform and reduce biological pro-

duction of normal marine macrofauna found in

outcrop studies. The palaeogeographical setting in

the Malm of SW-Germany, however, may lead to a

bias in palaeoenvironmental assessment using exclu-

sively macrofaunal assemblages because those are

preferentially preserved in reefal build-ups accessible

in outcrops. Marls and limestones from intra-reef

depressions are more subjective to intensive weath-

ering, not as well exposed and thus less well stu-

died. The reefs, although characteristic present-day

morphological features of the area are not fully

representative of the palaeoenvironments in local

depressions on the Eastern Bavarian Malm

Carbonate Platform, the so-called lagoons, troughs

or ``Wannen''.

Our samples are derived from such a location

where reef girdles surrounding an intra-reef de-

pression restricted water circulation in the lower

water body of the reef trough (Fig. 18). In the

upper water body above the reef top and above fair

weather wave base, free water circulation under

normal marine conditions prevailed and thus high

bioproductivity occurred. On the long term, only

minor salinity enhancement could develop on the

extended carbonate platform because episodic

storm events mixed the surface waters with normal

marine waters from the Tethys Ocean. In contrast,

within the sheltered intra-reef depression the waters

below storm wave based were continuously enriched

in salinity and density strati®cation developed. The

wall-reef surrounding the trough also e�ectively

prevented the input of terrigenous derived minero-

genic and organogenic debris which di�erentiates

this open marine from most other hypersaline

depositional settings.

In many other studies of hypersaline settings [see

thematic issues of Organic Geochemistry (1993) Vol.

20/8 and Organic Geochemistry (1995) Vol. 26/3] a

strong terrigenous derived organic component was


noted because of a restricted, land-locked lagoonal

environment. Such (sub)basins are often (i) almost

completely surrounded by land, (ii) connected tothe open sea by only a narrow and shallow passage

and (iii) separated from deeper marine settings by a

sill and thus susceptive to sealevel changes by eva-

poritic drawdowns and tectonic movements. Those

factors will inevitably lead to the accumulation ofterrigenous derived plant material, even if arid con-

ditions in the surrounding are not favorable for

extensive plant cover (Meyer and Schmidt-Kaler,

1989). Due to the special intra-reef setting of our

case study the terrigenous component is minimaland long chain n-alkane and alkylthiophene distri-

butions consequently re¯ect algal sources. A mi-

crobial rather than an algal contribution might be

indicated by the high abundance of C14-, C16- and

C18-n-alkanes. These compounds are likely to havebeen directly biosynthesized as saturated hydrocar-

bons because no functionalized lipids that incorpor-

ated reduced sulfur are present in the OSC.

Isolation of the intra-reef basin from terrigenous

minerogenic input consequently lead to an iron-

depleted environment that favoured incorporation

of sulfur in organic matter to produce OSC. In ad-dition, the protection of intra-reef sediments from

wave action and water column mixing by the sur-

rounding sponge reef girdle, stimulated oxygen de-

pletion and the establishment euxinic conditions via

activity of sulfate reducing bacteria. Surprisingly, aclear relationship between degree of sediment lami-

nation and degree of sulfurization could not be

detected. Comparable to a restricted lagoonal set-

ting the environmental changes must have occured

very frequently and de®nitely above the temporal

resolution covered by our sample set. This will be

one possible explanation why lithofacies does not

follow organic matter variations. Another pointmay be seen in the very rapid and irregular depo-

sition of micritic carbonates which seems to be

decoupled from main phases of organic matter sedi-

mentation. For the non-laminated marls and the

limestones it can be assumed that a major part ofsedimentation took place when storm events stirred-

up carbonate oozes produced on surrounding open

marine platform areas, which were then washed

over the reef-walls into the intra-reef depression.

The hopene distribution, the composition of iso-

prenoid thiophenes, the pristane/phytane-ratio and

also the partially the MTTC-ratio do indicate``higher than normal marine salinities''. Although

this is the exact de®nition of the term ``hypersaline''

(Kirkland and Evans, 1981), ``hypersaline'' has been

used to describe various other degrees of salinity.

We therefore de®ne the salinity range during depo-sition of the Malm z sediments as mesosaline sensu

Kirkland and Evans (1981) (for clarity note that the

term ``mesohaline'' in a Remane diagram de®nes a

hyposaline regime of 5 to 18-). We further restrict

the range of possible salinity variations to 40±80-,episodically reaching maxima of up to approxi-

mately 100-. On average, salinities >40- in the

uppermost water body of the intra-reef lagoon are

unlikely because they would have terminated

growth of the surrounding algal/spongal reefs. Apeak salinity of approximately 100- in the bottom

waters is assumed because higher values would ulti-

mately lead to gypsum deposition even during

short-term salinity oscillations and no indication of

such sulfate deposition is known. Some redissolu-

Fig. 18. Schematic diagram of the depositional setting during Malm z on the Southern BavarianCarbonate Platform, illustrating control of reef morphology on restriction. Surface waters on the plat-form are episodically mixed with fresh marine waters from the southernly Tethys Ocean during stormevents, which also supply large amounts of carbonatic oozes into the reef trough. During periods ofreduced mixing, slightly enhanced salinity develops on the platform and higher-density waters sinkdown and accumulate in the intra-reef depression. Morphology induced stagnant bottom water con-ditions are thus density-stabilized and anoxic conditions are easily established. Reef tops reach well intothe highly productive zone of surface water above fair weather wave base, where algae and cyanobac-teria may thrive. Microbial mats may ¯oat at the pycnocline and/or develop on the sediment surface.

This scenario ®ts an open water marine setting with local development of hypersaline conditions.


tion and carbonate replacement of gypsum crystals

may take place under extremely reducing con-

ditions, but a portion of originally precipitated gyp-

sum would persevere and no ghost crystals are

reported. Due to density strati®cation, salinities in

the lower water column of the intra-reef depressions

were much higher than in the surrounding plat-

form.

The organisms contributing to the organic matter

deposited were strictly marine and included photo-

synthetic algae and cyanobacteria as well a hetero-

trophic microbial community. Algal and microalgal

input is indicated by n-alkanes and isoprenoid thio-

phenes in the C21 to C27 range, steranes, sterenes

and especially the abundant monoaromatic steroids.

A dino¯agellate input is indicated by some minor

occurence of dinosterane in the desulphurized polar

fraction and by the high concentration of 4-methyl-

monoaromatic steroids in the free bitumen and is in

agreement with microscopically identi®able dino¯a-

gellate-derived calci®ed cysts (Keupp and

Neumann, 1996; Vliex and Schwark, 1998).

Algal and zooplanktonic contribution to the or-

ganic matter as revealed by steroid distribution is

extremly di�cult to assess for the Malm z due to

complex biological input and early diagenesis. The

steroids extracted from the immature organic mat-

ter (approximately 0.3% Rr) include a coexisting

suite of steranes, sterenes, spirosterenes, steradienes,

monoaromatic desmethyl- and 4-methylsteranes,

diaromatic steranes and some minor triaromatic

steranes (sterols and steroidal ketones are the sub-

ject of ongoing studies and will add even more com-

plexity to this picture). Several of the above

mentioned steroid classes were not previously

reported in the literature or their structures could

not be fully elucidated. Thus very special conditions

must have prevailed during deposition of the Malm

z sediments.

All observations point to an enhanced salinity

and strong reducing conditions. The paucity of

minerogenic detritus, in accordance with the lack of

rearranged steroids, leads to intensive sulfur incor-

poration into organic matter. Sulfur incorporation

into steroids however, as evidenced by the complete

lack of thiophenic steroids, either did not take place

or intermediately formed sulfurized steroids already

have had their sulfur released. The high amount of

available sulfur is furthermore assumed to have

promoted aromatization of steroids at this low

stage of maturity. Depending on double bond pos-

itions of biological precursor sterols, early diagen-

esis proceeded di�erently for C28-steroids as

compared to C27 and C29-counterparts. We noticed

signi®cant di�erences in the relative abundance of

the C27, C28 and C29 members for various steroid

classes as determined from the integration of

characteristic fragment ions. Most similar patterns

occur for the aaa-steranes, 5a-spirosterenes and dia-

romatic steroids with a clear predominance of C27

and C29 over the C28 analogues. The opposite pat-

tern with a predominance of C28 over C27 and C29

steroids is noted for the abb-steranes, the 5b-spiros-terenes and the regular monoaromatic steroids. The

sterenes and steradienes reveal a more evenly distri-

bution with a slight reduction in the amount of the

C27 compounds. Ongoing studies aimed to elucidate

the structure of the unknown sterenes and stera-

dienes will probably allow a better understanding

and re-interpretation of the early diagentic path-

ways prevailing during deposition of the Malm zsediments.

Although frequently silici®ed carbonates, alterna-

tions of cherts and carbonates and pure chert layers

occur, a diatomaceous input can be excluded for

the Malm z sediments, which is in accordance with

the total lack of saturated C20 and C25 HBI and

their respective thiophenic diagenesis products.

These compounds are very abundant in other

hypersaline settings but diatoms did not become

major contributors until the late Cretaceous and

thus were not present in the Jurassic samples stu-

died. Radiolaria and siliceous sponge rhaxes often

well preserved and identi®ed by REM as well as by

¯uorescence microscopy on polished blocks (Keupp

and Neumann, 1996; Vliex and Schwark, 1998) are

considered to be the source of biogenic silica.

Biomarkers speci®c for sponges and radiolaria are

not known and their contribution to extractable or-

ganic matter therefore can not be determined.

Cyanobacterial input is represented by short

chain n-alkanes and extended hopenes. For marl

lithologies, microscopical observations established a

close relationship between ¯uorescence behaviour of

cyanobacterial mats and extractable porphyrin ¯u-

orescence properties. Algal mats present in the car-

bonates contrastingly show a ¯uorescence

behaviour that is compatible with that of por-

phyrin-free maltene fractions. Hence, we consider

cyanobacteria as the main source for porphyrins in

the Malm M and ML lithofacies types.

The lack of aryl isoprenoids and di-aromatic

carotenoids or their condensation products in the

free aromatic as well as in the desulphurized polar

fractions indicates that during deposition of Malm

z marls no chlorobiaceae would thrive in the water

column of the intra-reef depression. This is surpris-

ing in that the relatively low water depth (<60 m)

and the high degree of sulfurization point towards

an extension of the euxinic realm well into the pho-

tic zone. Preliminary investigations of porphyrin

distributions (Turner, 1998, personal communi-

cation) revealed the presence of extended porphyr-

ins. Although precise structural elucidation is not

completed and coelution of chlorobiaceae derived

porphyrins with other isomers can not be fully

excluded, it thus seems very likely that photic zone

anoxia at least periodically prevailed in the Malm z


environment. The presence of gammacerane in thesulfur bound fraction would ®t into a scheme of

well-strati®ed water column and the existence of abacterial plate ¯oating at the chemocline.

CONCLUSIONS

Biomarker distribution of free and sulfur boundlipids indicates deposition of marine derived organic

matter for the Malm z sediments in theRennertshofen Trough in SW-Germany. Lack ofterrigenous input as revealed by n-alkane and terpe-

noid distribution lead to iron-limitation and prefer-ential incorporation of reduced sulphur intofunctionalized lipids. Local palaeogeography of the

intra-reef depression provided a restricted environ-ment on the open marine platform, thus leading tothe establishment of oxygen-depleted conditionsand via bacterial sulfate reduction to highly euxinic

conditions in the lower water body. Sulfurization oflipids was thus favoured by close spatial relation-ship between the euxinic and the photic zone.

An enhanced salinity of approximately 40±80-was recognized based on saturated isoprenoid, al-kylated thiophene and alkylated chroman distri-

bution. Correlation of pristane/phytane-ratios andITR is better than with the MTTC-ratio indicatingthat the ITR and the MTTC-ratio might re¯ect sal-inity conditions in di�erent parts of the water body.

High abundance of abb-steranes in the immaturesediments, as previously noted in hypersaline set-tings is restricted to the methylcholestanes, whereas

cholestanes and ethylcholestanes show maturityconcordant isomer distributions. Diagenetically in-termediate and labile sterene distributions are domi-

nated by spirosterens and unknown sterenes thatshow similar isomer distribution patterns for C27-and C29-members but a di�erent distribution for

the C28-compounds. A comparable compound pat-tern is noticed for structurally equivalent stera-dienes, occuring in the aromatic fraction. Di�erentearly diagenetic and/or dietary pathways further-

more lead to very low abundances of the C28-com-pound in a series of tentatively identi®ed A/B-ringdiaromatic steroids. Input of an speci®c C28 steroid

from a possibly more halotolerant precursor organ-ism seems likely, although particularly high cumu-lative abundances of C28 steroids due to improved

salinity adaption of the precursor were not encoun-tered. Alternatively a speci®c dietary pathway lead-ing to unusual C28-steroid distribution can not beexcluded. D7 sterenes quoted as possible precursor

for abb-steranes in hypersaline settings as well as D5

sterenes were not detected in the immature samples.Biological input from photosynthetic algae and

cyanobacteria was recognized by distribution ofsteroids and n-alkanes as well as alkyl-thiophenes.Organic matter derived from cyanobacteria is also

represented by abundant porphyrins. Diatoms often

signi®cant contributers to organic matter found inhypersaline settings were not fully evolved in the

Jurassic and thus C20 and C25 HBI compounds werenot to be detected. Terrigenous input at the studysite was extremely low but microbially derived or-

ganic matter is evident by hopanoids and especiallyby branched C19-thiophenes that originate fromstraight chain precursors with a 9-methyl-skeleton.

Biomarker distribution of desulphurized polarfractions show patterns compatible with free hydro-carbon fractions except for the exclusive occurence

of gammacerane in the bound fractions. Presence ofgammacerane might be taken as indication ofenhanced salinity coupled with highly reducing con-ditions. Complete quenching of the functionalized

gammacerane precursor by sulfurization in thepolar fraction points towards a close spatial re-lationship between habitat of precursor organism

and the euxinic zone, making an origin from ciliatesthriving from a bacterial plate ¯oating at the che-mocline most likely.

Organic petrology using UV-excitation revealedtwo types of organic mats present in the laminatedmarls. One type consists exclusively of macroalgae

the second contains algae and cyanobacteria. The¯uorescence properties of the cyanobacterial matorganoclasts are identical to the ¯uorescence prop-erties of isolated Ni- and V.O-porphyrins, whereas

the alginite ¯uorescence is identical to those of por-phyrin-free maltene fractions. Thus we concludethat porphyrins in the Malm z extracts originate

predominantly from cyanobacteria. We assume thatthis observation is a ®rst step into an improvedmicroscale localization of speci®c biomarkers in

complex built geological samples.

AcknowledgementsÐProvision of samples and discussionwith Dr R. K. F. Meyer and Dr. H. Schmidt-Kaler during®eld-work and core studies is most gratefully acknowl-edged. We thank R. Loesing and B. Spittho� for analyti-cal assistance. This work was carried out under auspicesof the ENOG (European Network of OrganicGeochemists) and bene®tted from discussion within thisgroup. ENOG consists of Laboratoire de Geochimie, IFP,Rueil Malmaison, France; Institute of Petroleum andOrganic Geochemistry, FZ Juelich, Germany; UniversiteÂLouis Pasteur, Strasbourg, France; NIOZ, Texel, TheNetherlands; Department of Environmental Chemistry,CID-CISC, Barcelona, Spain; Organic Geochemistry Unit,University of Bristol, U.K. and Geological Department,University of Cologne, Germany and receives fundingfrom the European Community.

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